1. Field of the Invention
The present invention relates a cam wheel assembly for use in a hinge structure and more particularly, to a high-durability cam wheel assembly, which is durable in use and has means to guide rotation of the movable member relative to the fixed member in a balanced manner.
2. Description of the Related Art
Many products that we use frequently have a hinged structure that allowing turning of two coupled members relative to each other. For example, a door uses a hinged structure so that the user can turn the door panel relative to the doorframe to open/close the access. There are many mobile electronic products using hinge structures. For example, a notebook computer, electronic dictionary or mobile video disk player uses hinge structures for allowing the cover member (which carries a LCD display panel inside) to be turned relative to the base member between an open position and a close position.
A hinged structure for the aforesaid application uses two interference members, for example, friction members or cam wheel members for causing a torsional friction force upon rotation of the movable member relative to the fixed member so that the cover member of the mobile electronic product can be positively positioned in the desired angle.
A cam wheel assembly for the aforesaid application generally comprises a fixed member and a movable member. The fixed member is mounted on an object, for example, a bracket around a shaft member. The movable member has a center mounting hole coupled to the shaft member for rotation with the shaft member relative to the fixed member. The durability of the cam wheel assembly can be known only after a 20,000˜25,000 cycles of open and close test. According to the aforesaid cam wheel assembly design, the bearing force of the movable member received during its rotation with the shaft member is concentrated on the periphery of the center mounting hole. Therefore, the periphery of the center mounting hole of the movable member wears quickly with use. When the periphery of the center mounting hole of the movable member starts to wear, the work life of the cam wheel assembly is shortened, and the cam wheel assembly will be unstable to provide the designed torsional force. Further, according to the aforesaid prior art design, the fixed member has a radially extending mounting portion and a pin extended from the radially extending mounting portion for fastening to the bracket. The radially extending mounting portion greatly increases space occupation of the cam wheel assembly in the mobile electronic product, bringing a space arrangement problem. Further, because the fixed member is supported on the bracket by means of the pin at the radially extending mounting portion, the connection between the fixed member and the bracket is not strong.